The present invention relates to weighted zero solids loss circulation and/or fluid loss systems, such as for the drilling industry, like oil field drilling and completion operations.
In one or more embodiments, the present invention relates to loss circulation fluids or loss circulation drilling fluids, and methods to control loss circulation fluids.
In the drilling of well bores with modern rotary well drilling apparatus and methods, the bore hole is normally kept filled with clean circulating drilling mud, or other drilling fluid, which washes and flushes the cuttings removed by the rotary bit from the bottom of the well bore. Drilling muds, or other drilling fluids, are pumped under pressure down the interior of the drill pipe and are forced out through openings in the drill bit, providing lubrication and wetting of the exposed surface, which increases the efficiency of the bit. The fluid then lifts the rock cuttings produced by the bit away from it and carries them up the annulus outside the string of drill pipe.
As the drilling mud, or other drilling fluid, passes up the annulus, it deposits a film or cake on the walls of the surrounding formation. This film or cake serves to seal small cracks or fissures, circa. 0.001-0.002″ size, in the formation and also decreases friction on the rotating string of drill pipe. The rock cuttings which are carried to the surface by the drilling mud, or other drilling fluid, are removed from the mud, or other drilling fluid, by various types of separators, e.g. shaker screens, centrifugal filtering systems, desilters, etc. The cleaned drilling mud, or other drilling fluid, is then recirculated.
Conventional drilling muds, or other drilling fluids, are of varied composition, depending upon the needs of the particular drilling operation. While most drilling muds are mixtures of fresh water with various clays, such as expansible bentonite clay, native clay and attapulgite clay, such muds may contain salt water, oil, oil emulsions, synthetic materials, such as polymeric additives, or combinations of such materials. The term “drilling mud”, as used herein, includes conventional drilling muds, and equivalent drilling fluids of the slurry type, such as cement slurries.
Additional components are often added to drilling muds to impart desired characteristics, such as added weight or increased viscosity. These components may function physically, as in the case of barite, which is added to increase weight; or chemically, as in the case of sulfuric acid or hydrofluoric acid as a deflocculent. The more complex drilling muds can be very costly and their loss can mean a substantial increase in the cost of drilling a well.
The particle size in common drilling muds can be from about 0.5 to 30 microns, with a small percentage (perhaps as much as 5%) of the particles being as large as 100 microns. The balance of the particles above this range can be removed in process of preparation and in separation of the rock cuttings prior to recirculation of the mud. Because of the constant cleaning and removal of larger particles, the drilling mud can bridge only very small fissures (less than 0.002 in.) within the formations as the muds are normally used.
When the formation penetrated by the well bore has openings or fissures larger than about 0.001-0.002″, the ordinary drilling muds will flow into the openings and escape from the well bore into the formation. This loss of drilling mud may be slow or rapid depending upon the degree of porosity or the size of the fissures or fractures in the formation. In more severe cases the loss of fluid may result in a drop in the hydrostatic head to the point of hydraulic pressure equalization, which may fall thousands of feet below the surface.
In this instance, several conditions may occur which endanger the drilling operation and result in considerable economic loss. In normal circumstances, the column of drilling mud assists in supporting the wall of the well bore. Therefore, when a well bore is partially or completely emptied of drilling mud, the well bore walls are deprived of the hydraulic pressure head of the column of drilling circulation fluid extending downward from the surface, and consequently there will be hundreds or even thousands of feet of unsupported well wall that will be free to slough off and to cave into the well bore. That sloughing off or caving in may stick or freeze drill pipe that may be in the well bore or casing that may be therein and which is in the process of being installed and cemented. This condition is at times so severe that wells have been abandoned, or must be redrilled, because of it.
Additionally, the drilling mud is weighted to accommodate the depth of hole which has been drilled. This is done to minimize the danger of unequal pressures allowing a formation to release a bubble of gas, or a surge of oil or water toward the surface, causing a blowout of the well.
When drilling mud is lost in a well bore, the formation penetrated may be under great pressure which, if sufficient to overcome the static head of drilling mud remaining in the well bore, will cause a blowout, endangering the well, the financial investment in it, and the lives and safety of the personnel on site.
Where casing is being installed and cemented in place or cement plugs are being installed or other cementing operations are taking place, Portland cement slurries are often employed and these slurries likewise become lost through porous or fractured formations penetrated by the well bore.
As oil and gas wells are being drilled to progressively greater depths in the earth the problem of preventing or curing lost circulation becomes increasingly difficult largely due to the high differential in pressures encountered in the formations penetrated by deep well bores.
Where the well bore has penetrated depleted porous oil and gas formations and the pressures therein have become largely exhausted, the differential pressures may be 10,000 p.s.i. on the borehole side, forcing the drilling mud or cement slurries into the porous formations.
Lost circulation of drilling fluids has been a problem since the earliest days of well drilling. Many methods have been tried to solve the problem and many materials have been used as additives for preventing lost circulation.
There are a variety of lost circulation additives which are used. In particular, lost circulation additives can be flakes, fibers, and granular.
Drilling fluids are formulated to intentionally seal porous formations during drilling in order to stabilize the borehole and to control fluid loss. However, formations are frequently encountered that are so porous as to increase the loss of drilling fluids beyond an acceptable limit despite the use of lost circulation additives. Furthermore, a borehole may penetrate a fracture in the formation through which most of the drilling fluid may be lost.
In order to close off large pores and fractures that drain drilling fluid from the borehole, it is necessary to place the loss circulation material at the proper location and to be able to clean up the well bore after treatment is completed. The present invention offers a method for accomplishing this in a borehole whether the well is being drilled with aqueous drilling fluids, oil based drilling fluids or synthetic based drilling fluids.
A disadvantage with many previous loss circulation fluids and drilling fluids is that they contain a large amount of solids (e.g., barite, hematite or ilmenite) from the various components present, such as the weighting materials or other materials used to plug the lost circulation zones, such as ground nut shells, ground fibrous materials or ground plastics such as polyethylene.
Thus, there is a need to provide drilling fluids, completion fluids, and loss circulation fluids that can be preferably solids-free or have low solids content in the drilling fluid in order to avoid or minimize one or more of the above-mentioned disadvantages.
There is also a need to insulate the annular space of a producing wellbore, after drilling and completion operations are conducted, with a fluid that can retain the heat up the production string to minimize the deposition of waxes or the formation of hydrates, and the like.
It is often desirable that this annular space fluid or packer fluid acts to insulate the production fluid from cooling too rapidly. This acts to prevent the production fluid from waxing out and depositing on a colder and higher section of the production tubing as the producing oil or condensate hydrocarbon falls below its cloud point and waxes out.
By reducing the viscosity of an annular space or packer fluid by increasing the viscosity increasing components such as polymers, or preferably enabling cessation of viscosity flow as with a gel structure, the thermal convection is also being reduced and thermal conduction can increase thereby enhancing the insulating properties of the annular space.